Airbnb may dominate headlines when it comes to budget-friendly travel. But long before the online market, there was the home exchange.

Travelers have been exchanging their home for someone else’s and staying for free in just about any city in the world for decades, first through photo books that circulated via snail mail starting in the 1950s and now online.

"Over the past 12 months, we've seen an explosion in peer-to-peer travel, as more and more [travelers] look to vacation in homes, not hotels," says Debbie Wosskow, CEO of Love Home Swap, one of the newest home exchange sites to hit the scene.

For avid travelers, the savings can quickly add up.

"I'd estimate we've saved at least $50,000 on hotel rooms over the past year alone," says Manhattanite Mark Francis, who has swapped more than 15 times through Love Home Swap, including stays in a four-bedroom chateau in the South of France and a four-bedroom house in the Hamptons. "It's a wonderful way to travel and we've become friends with so many of our swap partners."

Most home exchange sites tend to work the same way: you can browse for free, but must join to list your property. Once you find the swap you like, the actual details -- finalizing dates, knowing where to find the key, how to get around -- are all up to you. (Of course, you should also check with your landlord or broker to make sure you aren't breaking your lease or policy with a home exchange.)

This UK-based company claims more than 60,000 properties in 160 countries which, according to Wosskow, makes it the world's largest home exchange club. Properties range from small and stylish to ultra-luxurious, with the biggest markets in the U.S., UK, France, Italy and Spain.

Fee: Starting at $20 a month

Good for: Frequent hosts. A point system allows users to accumulate points when you have someone stay in your home, which can then be used to "buy" a stay at another place.

This UK-based company was founded in 1985 and concentrates entirely on home swaps -- no rentals or other arrangements are listed. Its 6,000-plus active members are in more than 90 countries. Some long-standing members have completed more than 80 swaps.

Fee: $35 for six months, $59 for a year (free two-week trial also offered)

HomeLink, which just celebrated its 60th year of operation, boasts more than 13,000 members worldwide. "Our members' properties range from studio apartments in Manhattan to luxury estates," says Katie Costabel, owner of the USA branch of the Belgium-based company. "My husband swapped his modest house on Oahu with a count and his castle just outside of Paris."

This Barcelona-based site specializes in swaps for families, with approximately 35,000 properties in 159 countries, including both home exchanges and rentals. The online Family Travel Guide includes family-friendly activities, parks, restaurants and shops for many cities, plus a map that pinpoints each location.

Fee: $29 monthly subscription, $180 yearly subscription

Good for: Those traveling with kids in tow. New families who register may be able to take advantage of special promotions.

Sample listing: 2-bedroom apartment for up to 6 people in the Canary Islands, Spain

Founded by Nadege Conger, the mother in a well-traveled academic family, in 2000, Sabbatical Homes caters primarily to academics but is open to all for home exchanges, as well as rentals, house sitting and sharing. Exchanges are available in 36 countries, with most of the nearly 700 properties located in the U.S., Canada and Europe.

Fee: $65/non-academics, $45/academics to post a home-offered listing for up to 14 months. $20/non-academics, free for academics to post a home-wanted listing

Good for: Students and teachers. Exchange dates are geared towards academic calendars, with semester-long and summer possibilities.

Sample listing: 1-bedroom flat for up to 3 people in Sarria, Barcelona, Spain